Method of charging a thermostatic system with a condensible and a noncondensible medium

ABSTRACT

The invention relates to a method and apparatus for charging a thermostatic system with condensible and noncondensible mediums such as Freon and nitrogen. The noncondensible medium is introduced first at a predetermined partial pressure followed by the introduction of a measured quantity of the condensible medium. An aspect of the invention involves a preliminary flushing of the system with nitrogen at the system testing pressure such that not only is the system purged of air but the system is tested at the same time.

0 United States Patent [151 3,653,414

Weidner 1 51 Apr. 4, 11972 54] METHOD OF CHARGING A 3,232,324 2/1966Sokol ..141/3 THERMOSTATIC SYSTEM WITH A 2 33%}: 3; 133g g essCONDENSIBLE AND A 2,684,805 7/1954 McBean.... NONCQNDENSIBLE MEDIUM2,527,136 10/1950 Kagi et a1. ..222/s7 x t i [72] lnven or Er c Weidner,Augustenborg, Denmark Primary Examiner Edward J Earls [73] Assignee:Danfoss A/S, Nordborg, Denmark Attorney-Wayne B. Easton [22] Filed: May11, 1970 ABSTRACT [21] Appl' 36312 The invention relates to a method andapparatus for charging a thermostatic system with condensible andnoncondensible [52] U.S. Cl ..l4l/4, 141/9, 141/49, mediums such asFreon and nitrogen. The noncondensible 141/63, 141/104 medium isintroduced first at a predetermined partial pressure [51] Int. Cl ..B65b31/02 followed by he introduc ion of a measured quantity of the [58]Field of Search ..73/368.2, 368.4, 368.6; n n i le medi m- An a pe ofthe inv ntion involves a 141/1-5, 7-9, 1 1, 18, 20, 31, 37, 39, 47, 49,63, 61, preliminary flushing of the system with nitrogen at the system66, 82, 104, 197; 222/3, 4, 57 testing pressure such that not only isthe system purged of air but the system is tested at the same time. 56]References Cited 1 Claim, 1 Drawing Figure UNITED STATES PATENTS2,780,899 2/1957 Benson et al ..l41/3 X Patented April 4, 1972 73,653,414

31 :lt 20\ Ti: 1;:

METHOD OF CHARGING A THERMOSTATIC SYSTEM WITH A CONDENSIBLE AND ANONCONDENSIBLE MEDIUM The invention relates to a method of charging athermostatic system with a condensible and a noncondensible medium,andto a charging apparatus for performing this method.

In the case of thermostatic systems which consist for example of atemperature sensor and a working element connected thereto by way of acapillary tube, it is known to use charge materials which consist of amedium which is condensible over a working temperature range and of amedium which is not condensible over a working temperature range. Amongthe condensible media are sulphur dioxide and halogenized hydrocarbonssuch as methyl chloride or the substances marketed under the trade namesFreon or Frigen. Nitrogen or another inert gas is used as thenoncondensible medium.

For the purpose of charging the thermostatic system, it is firstevacuated, filled with the condensible medium in vapor form and thencharged with the noncondensible medium to the point at which therequired total pressure is reached. Surprisingly, in the majority ofcases the required temperaturepressure, curves that would be expected asthe result of the charged quantity of condensible medium, have not beenobtained. Frequently, the curves obtained have even diverged from eachother.

The object of the invention is to provide a charging method whichprovides perfectly reproducible results and enables the performance ofthe method to be still further simplified.

According to the invention, this object is achieved by first chargingthe noncondensible medium into the system and then the condensiblemedium.

The invention is based upon the heretofore unobserved fact that thecondensible medium, which is first filled into the system and is invapor form, partially condenses under the pressure at which thenoncondensible medium is charged into the system so that the condensiblemedium thus undergoes considerable reduction in volume. Consequently, ahigher proportion of noncondensible medium is charged into the systemthan corresponds to the required quantitative ratio. Furthermore, thequantity of the condensate is very much dependent upon temperature.Slight changes in the charging conditions, e.g. in the room temperature,lead to clearly differing temperature-curves. If on the other hand, inaccordance with the invention, the system is first charged with thenoncondensible medium, this risk is no longer run, since its volume candiminish only in dependence upon the charging pressure but not as aresult of condensation. Thus there arise no difficulties in filling thethermostatic system with a measured quantity of the condensible medium.

This can be done for example by charging the noncondensible medium intothe system up to a partial pressure corresponding to the required mixratio and then charging the condensible medium in a measured quantity.For example, a quantity of liquid condensate, measured in a measuringchamber, can be charged into the thermostatic system. For practicalpurposes it is simplest to measure the condensible medium in thesuperheated condition and to fill it into the system.

A particular advantage is obtained here if at least part of thethermostatic system is cooled. This ensures that the condensible mediumis condensed at this cooled part and passes into the thermostatic systemrapidly and as completely as required.

The normal use of nitrogen as the noncondensible medium offersparticular advantages. The system can then be flushed with nitrogenbefore being charged with the required quantity of nitrogen. This avoidsthe need for the considerably more expensive evacuation of thethermostatic system. Flushing does not need to be carried out with verygreat intensity, since the air previously filling the system will havealready had a nitrogen content of approximately 78 percent.

It is for example sufficient if the flushing operation is carried out bycharging the system with nitrogen at an excess pressure and thenrelaxing the pressure. The flushing operation can be repeated severaltimes if required. During each flushing operation parts of theunrequited gases are mixed with pure nitrogen and parts of this mixtureare blown out again during the subsequent relaxation of pressure, sothat the unrequired gases are reduced to a fraction of the proportionpreviously present each time.

If the flushing pressure is raised to the test pressure for the system,not only is a particularly good flushing effect achieved, but thecompressive strength of the system is tested at the same time.

After at least one flushing operation, a pressure of similar magnitudecan be applied to the other side of the movable part of the system, e.g.the diaphragm or bellows. This reinforces the flushing action, since apumping action is applied to the contents of the system by the returnmovement of the diaphragm or of the bellows. Furthermore, the propertiesof the material of the diaphragm or bellows are improved by theapplication of pressure on both sides as compared with unilateralloading.

A charging apparatus for performing the method of the invention ischaracterized by a first container for the pressurized noncondensiblemedium and a first pipe which extends therefrom and to which a pressuregauge is connected, in addition to a charging head, and which can beblocked by means of valves when the pressure gauge indicates apredetermined value, the apparatus also being characterized by a secondcontainer for pressurized condensible medium, from which container asecond pipe, incorporating a measuring device which can be blocked bymeans of valves, runs to the charging head. By actuating the valves inthe first pipe in dependence upon the value indicated by the pressuregauge, the noncondensible medium can be charged into the thermostaticsystem through the charging head at a predetermined pressure. Actuationof the valves in the second pipe enables the system, with the help ofthe metering device, then to be charged with the required quantity ofcondensible medium.

The second pipe can be connected to the second container at the bottomfor example, and the metering device can consist of a liquid-measuringvessel. This arrangement is particularly suitable when fairly largequantities of the condensible medium have to be filled into the system.In an alternative arrangement, the second pipe can be connected to thetop of the second container and the metering device can consist of ameasuring chamber with a pressure gauge connected thereto. lfsuperheated medium is introduced into the measuring chamber, which has apredetermined volume, until a first pressure that can be read off on thepressure gauge is reached, and is then passed into the thermostaticsystem until the pressure has dropped to a predetermined second value,this ensures that a precisely defined quantity of the condensible mediumhas passed into the thermostatic system. This metering device isparticularly suitable for introducing small quantities of thecondensible medium. This is desirable for example in the case ofthermostatic systems in which it is intended to limit pressure bycompletely vaporizing the condensible medium at a limiting value fortemperature that is somewhat beyond the working range.

The charging operation can also be rendered automatic if the pressuregauge actuates contacts which close the inlet valve at a predeterminedfirst pressure and, if required, open the outlet valve and, at apredetermined lower second pressure, close the outlet valve and open theinlet valve.

Expediently, a reducing valve is fitted on the output side of the secondcontainer. In this way the condensible medium can be stored in theliquid state and under a relatively high pressure, and after relaxationof the pressure in the reducing valve, the medium is always availablewith a sufficient degree of superheat.

The invention will now be described in more detail by reference toequipment suitable for the charging method. This equipment isillustrated schematically in the drawing.

A thermostatic system consists of a sensor 1, a working element 2, acapillary tube 3 connecting these two components, and a capillarycharging port 4. The working element comprises a case 5 and a diaphragmelement 6. The diaphragm can bear against the two halves of the case inits two end-positions. For charging purposes, the sensor is connected toa charging head 9 by way of the capillary charging pipe 4. This head 9is connected to a pipe 8. The working element controls a valve havingtwo compartments 10 and 11. These two compartments communicate with aconnecting pipe 12.

Nitrogen under very high pressure, and in particular the test pressurefor the thermostatic system, is present in the container 13. Thisnitrogen container 13 is connected to each of the pipes 15 and 16 by wayofa reducing valve 14. The pipes 15 and 16 contain magnetic valves 17and 18, the magnetic valve 18 monitoring the connecting pipe 12. Fittedin the connecting pipe 12 is a further magnetic valve 19 which opens toatmosphere. This magnetic valve 19 is used for discharging nitrogen andair mixed therewith which is flushed from the system. The magnetic valve17 communicates with the charging pipe 8 by way of a pipe 20, to whichis connected a pressure gauge 21, and by way ofa magnetic valve 22.

A container 23 is partly charged with the condensible medium. The vaporwhich corresponds to the pressure at room temperature, passes by way ofa reducing valve 24 to a pipe 25, which is connected to a measuringcontainer 27 by way of a magnetic valve 26. Connected to the measuringcontainer 27 is a pressure gauge 28. The outlet of the container isconnected to a pipe 30 through a magnetic valve 29. The container 23,the measuring container 27 and the associated parts can also be replacedby another container 31 to the base of which is connected an outlet pipe32 which leads, by way ofa valve 33, to a measuring container 34 forfluid. The outlet of this container is connected to the pipe 30 througha valve 35. The charging pipe 8 also communicates with the atmospherethrough a valve 36 and, if required, can be connected to a vacuum pump38 by way of a further valve 37. The charging operation can proceed inthe following way: Firstly it is assumed that the thermostatic system isconnected to the charging apparatus through its charging port 4. Thevalves 17 and 22 are then opened. The pressure is automaticallydetermined by the reducing valve 14; the pressure so established obtainsin the pipes and thus also in the sensor 1 and in the entirethermostatic system. This pressure can be as great as 28 atmos. forexample, this corresponding to the test pressure for the system. The aircontained in the pressure is therefore compressed to a fraction of itsoriginal volume. The air thus mixes with the nitrogen. The valve 22 isthen closed and the valve 36 opened. Part of the nitrogen-air mixturecan escape therethrough, and the pressures drops to that of theatmosphere. At this moment only about one-thirtieth of the unrequiredatmospheric air is contained in the charge gas. Where nitrogen is usedas the charge gas, the proportion of gases other than nitrogen is lessthan 1 percent. This quantity is generally permissible. On the otherhand however the proportion of foreign gases can be still furtherreduced by a further similar flushing operation. At the same time themagnetic valve 18 is opened, nitrogen flowing at the same pressure intothe compartments l0 and 11 by way of the pipe 12. This pressure ismaintained while the valve 36 is opened. In this way this pressurereinforces the emptying of the diaphragm case by way of the sensor andmagnetic valve 36. Here, it is of particular advantage for this to takeplace in the diaphragm casing from which, in the normal way, atmosphericair is most difficult to remove.

These high pressures also enable a simultaneous check to be carried outto determine whether the system is fluid-tight. If the case 5 is loadedwith the same pressure on both sides, then by simply immersing theentire valve body in a liquid, it is possible to ascertain whetherleaking elements are present, since gas bubbles will occur if they are.Furthermore, the test pressure provides the very considerable advantagethat the stresses, which may occur during the welding of a diaphragmelement, are compensated by these pressure conditions. The service lifeof the element is extended by this compensation of the stresses.

The partial pressure of the nitrogen in the system is then adjusted tothe required value. For this purpose, the magnetic valve 18 is closedand the magnetic valve 19 opened. If the thermostatic system is nowunder excess pressure and the magnetic valve 17 is closed, the pressuregauge 21 can be used to set the pressure if a partial pressure of thenitrogen above that of the atmosphere is required. If this pressure isto be below atmospheric pressure, then instead of the valve 36, a vacuumpump 38 can be connected by way of the magnetic valve 37, the desiredreduced pressure being produced, whereafter the valve 36 or 37 and thevalve 22 are closed again.

The system can now be charged with the condensible medium. If the systemis charged with a liquid condensible medium, a quantity of liquid isallowed to flow from the container 31 through the valve 33 and into themeasuring container 34, the valve 35 being closed. As little as a fewcm. or even fractions of a cm. can be measured in the measuringcontainer. When a certain charge level is reached, the valve 33 isclosed. Thereafter, the valve 35 is opened until the charge level hasdropped to a point at which it corresponds to the required chargequantity. The condensate then flows through the charging port 9 into thesensor 1 and is there mixed with the noncondensible medium present. Incertain cases it is advisable to cool the sensor or the thermostaticsystem in proportion to the room temperature, so that the condensiblemedium can also pass into the thermostatic system in a reliable manner.

A still more advantageous method can be used in the case of smallquantities of condensible medium, e.g. when pressurelimited valves areused, by measuring off superheated vapor. This takes places in thefollowing manner: a liquid condensible medium is present in thecontainer 23 at room temperature. Saturated vapor is formed above thismedium and the pressure thereof corresponds to the room temperature.This saturated vapor can now flow into the pipe 25 through anautomaticallyoperating pressure-reducing valve, the saturated vaporsbecoming superheated and passing through the open magnetic valve 26 intothe measuring container 27. The pressure gauge 28 fitted at this pointshows what is the pressure of the superheated gas at room temperature.The magnetic valve 26 is then closed and the magnetic valve 29 opened.The superheated gas can then flow from the container 27 to thethermostatic system, an at a certain drop in pressure, indicated by thepressure gauge 28, the magnetic valve 29 is closed again. In this caseit is advisable to keep the sensor below room temperature, e.g. by meansof a cooling device. This superheated gas then immediately condenses onthe cooler part of the system, and it passes into the thermostaticsystem in a reliable manner. In this way, very small quantities can bereadily determined, since the volume of the container 27 is adapted tosuit the quantity of condensible medium that is to be charged into thesystem, and thus a measurable quantity is reached based on the knownequation of state for the gases. Compared with direct charging with theliquid medium, this method offers the advantage that even when therequired quantity is very small and almost incapable of being measured,very accurate charging can be achieved since occasionally droplets canadhere to the walls of the measuring container due, for example, toadherence of liquid to the container walls. In the case of athermostatic expansion valve with a pressure limit directly at freezingpoint, this is of considerable advantage since often only a spot ofcondensate will be present in the subsequently closed thermostaticsystem.

Thereafter, the charging port 4 is clamped together by means of jaws andis then soldered up. In this system there is no need to check whetherthe correct quantity has in fact entered, since it is not possible forthe noncondensible medium now to compress the superheated vapor of thecondensible medium and thus for an uncontrolled quantity ofnoncondensible medium to be charged into the system. It is obvious thatthe pressure in the container 27 must be higher than the pressure at thepressure gauge 21 after the noncondensible medium has been introduced.Thus a very accurate charge quantity is obtained in the thermostaticsystem, since the volume of the system is known and is first chargedonly with superheated gas in the form of nitrogen. Then, the rest of thecharge, which can simply be read off from the pressure-drop at thecontainer 27, is introduced.

If the pressure gauge 28 is provided with contacts, it can directlycontrol the valves 28 and 29. If the valve 26 is opened and the valve 29closed, the pressure in the container 27 rises until the pressure gaugereaches an upper limiting value. At this value, the valve 26 is closed.When the valve 29 is later opened for charging the thermostatic system,the pressure in the container 27 drops until, at a lower limiting value,the valve 29 is closed. When charging takes place on an assembly line,the pressure gauge 28 can also open the valve 29 at the upper limitingvalue and the valve 26, possibly after a time-lag, at the lower limitingvalue.

lclaim:

1. A method of charging a thermostatic system with a condensible mediumand a noncondensible medium comprising the steps of firstly charging thesystem with said noncondensible medium and secondly charging said systemwith said condensible medium, said noncondensible medium being chargedinto said system at a predetermined pressure, said condensible mediumbeing charged into said system in a measured quantity, saidnoncondensible medium being nitrogen, the method including the step offlushing said system with nitrogen at least once prior to said step ofcharging said system with said noncondensible medium, said systemincluding a working element having a moving part with chambers onopposite sides thereof and a sensor bulb connected with a capillary tubeto one of said chambers, said method including the step of directingnitrogen to the other of said chambers subsequent to said step offlushing said system

1. A method of charging a thermostatic system with a condensible mediumand a noncondensible medium comprising the steps of firstly charging thesystem with said noncondensible medium and secondly charging said systemwith said condensible medium, said noncondensible medium being chargedinto said system at a predetermined pressure, said condensible mediumbeing charged into said system in a measured quantity, saidnoncondensible medium being nitrogen, the method including the step offlushing said system with nitrogen at least once prior to said step ofcharging said system with said noncondensible medium, said systemincluding a working element having a moving part with chambers onopposite sides thereof and a sensor bulb connected with a capillary tubeto one of said chambers, said method including the step of directingnitrogen to the other of said chambers subsequent to said step offlushing said system.